This invention relates to the field of electrical cable splicing. More particularly, this invention relates to techniques for providing insulated splices for high voltage cables and the like.
High voltage cables used to transmit large quantities of electrical power either above ground or underground frequently require splicing either during installation or during repair. The following commonly assigned pending U.S. patent applications disclose several techniques used for splicing cables: Serial No. 334,103 filed Feb. 20, 1973 for "MOLDING APPARATUS FOR SPLICING ELECTRICAL CABLE" Serial No. 541,298 filed Jan. 15, 1975 for "CABLE MOLDING APPA- RATUS AND METHOD" Serial No. 545,948 filed Jan. 31, 1975 for "MOLDING METHOD FOR SPLICING ELECTRICAL CABLE"
Typically, in making a splice the ends of the two cables to be spliced together are first prepared by removing a portion of the outer cable jacket, folding back the electrically conductive outer metallic shield, removing a portion of the underlying outer semiconducting screen, penciling the cable insulation down to the inner semiconducting screen, and removing a portion of the inner semiconducting screen to expose the central conductors. The two exposed central conductor end portions are next mechanically and electrically coupled together by means of a conventional connector, e.g., a connector sold in the trade as a CADWELD connector. The splice is next covered with one or more layers of semiconducting tape, and an electrically insulative jacket is molded onto the splice and adjacent regions of the cable insulation, after which a layer of semiconducting material is applied to the outer surface of the insulative mold, a layer of metal gauze material is wrapped around the semiconductive material, secured in place and soldered to the electrically conductive outer metallic shield and the splice is finished off with a layer of conventional electrician's tape.
The insulative jacket is molded to the cable splice by wrapping strips of semiconducting molding compound over the semiconducting tape, wrapping strips of electrically insulative thermosetting molding compound over the wrapped semiconducting molding material, placing the wrapped splice into a mold cavity having end clamp portions at opposed ends, closing and heating the mold cavity to soften the wrapped layers while supplying additional insulative molding compound under heat and pressure into the mold chamber to soften the semiconducting and insulative molding compounds and bond them to the various surfaces with which they make contact, and curing the molded splice. Since both the molding compound and the cable insulation material typically possess a high coefficient of thermal expansion, the end clamp portions are provided with an inner radius larger than the outer radius of the cable insulation in order to permit softened compound and material to egress from the mold cavity during the molding process.
Cable splices prepared in the above fashion have been found to function well in many applications. However, in some cases, internal mold pressure during the heat-molding process increases to a value at which cable deformation, and in severe cases, cable rupture, occurs. In other cases, the internal mold pressure during the heat-molding process does not attain a value sufficient to properly cure the splice or to avoid undesirable gas entrainment in the splice. Efforts to provide a low cost method and apparatus capable of ensuring suitable mold pressures have not met with wide success to data.